Isotope effect on the anomalies of water: a corresponding states analysis

Abstract

Light and heavy water show similar anomalies in thermodynamic and dynamic properties, with a consistent trend of anomalies occurring at higher temperature in heavy water. Viscosity also increases faster upon cooling in heavy water, causing a giant isotope effect, with a viscosity ratio near 2.4 at 244 K. While a simple temperature shift apparently helps in collapsing experimental data for both isotopes, it lacks a clear justification, changes value with the property considered, and requires additional ad hoc scaling factors. Here we use a corresponding states analysis based on the possible existence of a liquid-liquid critical point in supercooled water. This provides a coherent framework which leads to the collapse of thermodynamic data. The ratio between dynamic properties of the isotopes is strongly reduced. In particular, the decoupling between viscosity $\eta$ and self-diffusion $D$, measured as a function of temperature $T$ by the Stokes-Einstein ratio $D\eta /T$, is found to collapse after applying the corresponding states analysis. Our results are consistent with simulations and suggest that the various isotope effects mirror the one on the liquid-liquid transition.

11 pages, 11 figures. Added corresponding states analysis of isobaric heat capacity, discussion of Stokes-Einstein ratio under pressure, citation to Sutherland's works, more detailed figure captions, and minor edits. The following article has been accepted by the Journal of Chemical Physics. After it is published, it will be found at https://doi.org/10.1063/5.0205452

References in corpus (3)

• Compressibility anomalies in stretched water and their interplay with density anomalies
• Thermodynamics of Fluid Polyamorphism
• Shear viscosity and Stokes-Einstein violation in supercooled light and heavy water